Frequency variable compressor and control method thereof

ABSTRACT

The present invention discloses a frequency variable compressor, including a shell defining an airtight space, an accumulator temporarily storing refrigerant before introducing the refrigerant into the shell, a first compression mechanism unit positioned in the shell, including a rolling piston, a cylinder, a refrigerant suction hole, a refrigerant discharge hole and a vane, and compressing refrigerant, a second compression mechanism unit positioned in the shell, including a rolling piston, a cylinder, a refrigerant suction hole, a refrigerant discharge hole and a vane, and compressing refrigerant, a frequency variable motor positioned in the shell and transferring power to the rolling pistons of the first and second compression mechanism units through a rotating shaft, and a valve controlling the flow of the refrigerant such that the first and second compression mechanism units compress the refrigerant by a twin rotary compressor type or a 2-stage rotary compressor type.

TECHNICAL FIELD

The present invention relates to a frequency variable compressor.

BACKGROUND ART

In general, a compressor is a mechanical apparatus receiving power from a power generation apparatus such as an electric motor, a turbine or the like, and compressing the air, refrigerant or various operating gases to raise a pressure. The compressor has been widely used for electric home appliances such as refrigerators and air conditioners, and the application thereof has been expanded to the whole industry.

The compressors are roughly classified into a reciprocating compressor in which a compression space into/from which an operating gas is sucked and discharged is defined between a piston and a cylinder and the piston is linearly reciprocated in the cylinder to compress refrigerant, a rotary compressor in which a compression space into/from which an operating gas is sucked and discharged is defined between an eccentrically-rotated roller and a cylinder and the roller is eccentrically rotated along an inside wall of the cylinder to compress refrigerant, and a scroll compressor in which a compression space into/from which an operating gas is sucked and discharged is defined between an orbiting scroll and a fixed scroll and the orbiting scroll is rotated along the fixed scroll to compress refrigerant. Particularly, the rotary compressor has been developed into a twin rotary compressor including two rollers and two cylinders at its upper and lower portions, in which the upper and lower roller and cylinder pairs compress some and the rest of the total compression capacity, and a 2-stage rotary compressor including two rollers and two cylinders at its upper and lower portions, in which the two cylinders communicate with each other, one pair compresses relatively low-pressure refrigerant, and the other pair compresses relatively high-pressure refrigerant undergoing the low-pressure compression stage.

Korean Registered Patent Publication No. 1994-0001355 discloses a rotary compressor. A motor is positioned in a shell and a rotating shaft is installed to penetrate through the motor. In addition, a cylinder is positioned below the motor, and an eccentric portion fitted around the rotating shaft and a roller fitted into the eccentric portion are positioned in the cylinder. A refrigerant outlet hole and a refrigerant inlet hole are formed in the cylinder, and a vane preventing low-pressure non-compressed refrigerant from being mixed with high-pressure compressed refrigerant is installed between the refrigerant outlet hole and the refrigerant inlet hole.

Moreover, a spring is installed at one end of the vane to maintain the eccentrically-rotated roller and the vane to be in contact with each other.

When the rotating shaft is rotated by the motor, the eccentric portion and the roller are rotated along the inner circumference of the cylinder to compress refrigerant gas. The compressed refrigerant gas is discharged through the refrigerant outlet hole.

Korean Laid-Open Patent Publication No. 10-2005-0062995 discloses a twin rotary compressor. Referring to FIG. 1, the twin rotary compressor includes two cylinders 1035 and 1045 compressing the same capacity and a middle plate 1030, and thus doubles a compression capacity as compared with a 1-stage compressor.

Korean Laid-Open Patent Publication No. 10-2007-0009958 discloses a 2-stage rotary compressor. Referring to FIG. 2, a motor unit 2014 having a stator 2007 and a rotor 2008 is provided at an inside upper portion of a hermetic container 2013 of a compressor 2001, and a rotating shaft 2002 connected to the motor unit 2014 is provided with two eccentric portions. A main bearing 2009, a high-pressure compression element 2020 b, a middle plate 2015, a low-pressure compression element 2020 a and a sub bearing 2019 are successively stacked from the motor unit side 2014 with respect to the rotating shaft 2002.

Additionally, a middle pipe 2040 is provided to introduce refrigerant compressed in the low-pressure compression element 2020 a into the high-pressure compression element 2020 b.

The rotary compressor includes a frequency variable motor with a variable operating frequency as the motor unit. The operating frequency of the frequency variable motor is varied according to changes in the cooling capacity required of the compressor, thereby varying the compression capacity of the compressor. A control unit controlling the compressor receives an input of the cooling capacity required of the compressor or senses the cooling capacity and controls an output frequency through a converter and an inverter. Here, the converter receives an input of commercial power AC and converts the AC into DC to rectify a commercial frequency into the DC, and the inverter re-converts the DC into a desired AC voltage/frequency. In addition, the frequency variable motor, which is the motor unit, drives a compression mechanism unit of the compressor at a frequency controlled by the control unit using the AC frequency-converted by the inverter.

FIG. 3 is a graph of efficiency and yearly operating time of a compressor including a conventional DC frequency variable motor as a motor unit by cooling and heating loads (operating frequencies). Referring to the graph, a variable speed DC inverter compressor generally used for heating and cooling operations has the maximum efficiency during the mid to high speed operation.

However, the variable speed DC inverter compressor has the longest yearly operating time in the low to mid speed range. Therefore, it is necessary to improve the performance of the variable speed DC inverter compressor during the low to mid speed operation of a large air-conditioning load and high using frequency.

DISCLOSURE Technical Problem

The present invention has been made in an effort to solve the above-described problems of the prior art, and an object of the present invention is to prevent reduction of energy efficiency of a frequency variable motor, when an inverter compressor using a DC frequency variable motor as a motor unit operates the frequency variable motor at a low speed to generate a low compression capacity as required.

Another object of the present invention is to provide a frequency variable compressor and a control method thereof which can control the total compression capacity of a compression mechanism unit by controlling two compression mechanism units driven by an inverter compressor to selectively compress refrigerant by either a twin compression method or a 2-stage compression method according to a cooling capacity required of the compressor, aside from controlling an operating frequency of a frequency variable motor.

A further object of the present invention is to provide a frequency variable compressor and a control method thereof which can improve energy efficiency in a small compression capacity by controlling two compression mechanism units to compress refrigerant by a 2-stage compression method, instead of decelerating the speed of a DC frequency variable motor, when a small compression capacity is required of the compressor.

A still further object of the present invention is to provide a frequency variable compressor and a control method thereof which can improve efficiency of the compressor by controlling a compression mechanism unit to compress refrigerant by a 2-stage compression method, when a small compression capacity is required of the compressor and a DC frequency variable motor is operated at a low speed.

Technical Solution

According to an aspect of the present invention for achieving the above objects, there is provided a frequency variable compressor, including: a shell defining a hermetic space; a plurality of compression chambers provided in the shell and compressing refrigerant therein; a frequency variable motor generating power to compress the refrigerant in the compression chamber; and a valve controlling the flow of the refrigerant sucked into and discharged from the plurality of compression chambers to sequentially or concurrently compress the refrigerant in the plurality of compression chambers.

In addition, the plurality of compression chambers are formed in a compression mechanism unit including a rolling piston and a cylinder.

Moreover, two or more of the plurality of compression chambers are two spaces separated by a barrier in one compression mechanism unit.

Further, the plurality of compression chambers are formed in two or more compression mechanism units.

Furthermore, the frequency variable compressor further includes a plurality of passages through which the refrigerant is sucked into or discharged from the plurality of compression chambers, wherein the valve changes the refrigerant suction or discharge direction in the passages.

Still furthermore, the frequency variable compressor further includes a plurality of passages through which the refrigerant is sucked into or discharged from the plurality of compression chambers, wherein the valve connects or disconnects the plurality of passages to/from one another.

Still furthermore, the frequency variable compressor further includes a control unit controlling the valve to sequentially compress the refrigerant in two or more of the plurality of compression chambers by multiple stages, when a frequency of the frequency variable motor is controlled at a frequency below a mid frequency.

Still furthermore, one or more of the plurality of compression chambers are connected to an inner passage through which the compressed refrigerant is discharged into the shell and a mid-pressure passage through which the compressed refrigerant is discharged to the valve side, and the valve connects or disconnects the mid-pressure passage to/from a passage through which the refrigerant is sucked into another of the plurality of compression chambers.

According to another aspect of the present invention, there is provided a frequency variable compressor, including: a shell defining a hermetic space; a first compression mechanism unit positioned in the shell, including a rolling piston, a cylinder, a refrigerant suction hole, a refrigerant discharge hole and a vane, and compressing refrigerant; a second compression mechanism unit positioned in the shell, including a rolling piston, a cylinder, a refrigerant suction hole, a refrigerant discharge hole and a vane, and compressing refrigerant; a frequency variable motor positioned in the shell and transferring power to the rolling pistons of the first and second compression mechanism units through a rotating shaft; a first suction passage through which the refrigerant is sucked into the first compression mechanism unit; a first discharge passage through which the refrigerant is discharged from the first compression mechanism unit; a second suction passage through which the refrigerant is sucked into the second compression mechanism unit; a mid-pressure passage connecting the second suction passage to the first discharge passage; and a valve provided on the mid-pressure passage and the second suction passage, connecting and disconnecting some part of the second suction passage to/from the mid-pressure passage, and closing and opening the rest of the second suction passage.

According to a further aspect of the present invention, there is provided a frequency variable compressor, including: a shell defining a hermetic space; an accumulator temporarily storing refrigerant before introducing the refrigerant into the shell; a first compression mechanism unit positioned in the shell, including a rolling piston, a cylinder, a refrigerant suction hole, a refrigerant discharge hole and a vane, and compressing refrigerant; a second compression mechanism unit positioned in the shell, including a rolling piston, a cylinder, a refrigerant suction hole, a refrigerant discharge hole and a vane, and compressing refrigerant; a frequency variable motor positioned in the shell and transferring power to the rolling pistons of the first and second compression mechanism units through a rotating shaft; a first suction passage through which the refrigerant is sucked into the first compression mechanism unit; a first discharge passage through which the refrigerant is discharged from the first compression mechanism unit into the shell; a second suction passage through which the refrigerant is sucked into the second compression mechanism unit; and a 4-way valve controlled such that the refrigerant discharged to the first discharge passage is selectively sucked into the second suction passage or discharged into the shell, two valve holes being positioned on the second suction passage, the other two valve holes being positioned on the first discharge passage.

In addition, the frequency variable compressor further includes a check valve positioned on the first discharge passage and the second suction passage.

According to a still further aspect of the present invention, there is provided a control method of a frequency variable compressor including a plurality of compression chambers, a frequency variable motor, a valve controlling the flow of refrigerant sucked into and discharged from the plurality of compression chambers, and a control unit controlling the valve, the control method including, when an operating frequency of the frequency variable motor is below a mid frequency, controlling the valve to compress the refrigerant in the plurality of compression chambers by multiple stages.

Moreover, the control method includes, when a small compression capacity is required of the compressor, controlling the operating frequency of the frequency variable motor at a low frequency.

According to a still further aspect of the present invention, there is provided a control method of a frequency variable compressor, including: controlling an operating frequency of a frequency variable motor according to a required compression capacity; and, when the operating frequency of the frequency variable motor is below a determined frequency, controlling a valve to compress refrigerant by either a parallel compression method for concurrently compressing the refrigerant in a plurality of compression chambers or a multi-stage compression method for sequentially compressing the refrigerant in the plurality of compression chambers.

In addition, the controlling of the operating frequency of the frequency variable motor is continuously repeated according to changes in the required compression capacity and the compression method.

According to a still further aspect of the present invention, there is provided a frequency variable compressor, including: a shell defining a hermetic space; an accumulator temporarily storing refrigerant before introducing the refrigerant into the shell; a first compression mechanism unit positioned in the shell, including a rolling piston, a cylinder, a refrigerant suction hole, a refrigerant discharge hole and a vane, and compressing refrigerant; a second compression mechanism unit positioned in the shell, including a rolling piston, a cylinder, a refrigerant suction hole, a refrigerant discharge hole and a vane, and compressing refrigerant; a frequency variable motor positioned in the shell and transferring power to the rolling pistons of the first and second compression mechanism units through a rotating shaft; and a valve controlling the flow of the refrigerant such that the first and second compression mechanism units compress the refrigerant in a twin rotary compressor type or a 2-stage rotary compressor type.

In addition, the frequency variable compressor further includes a passage through which the refrigerant is sucked into or discharged from the first and second compression mechanism units, wherein the valve changes the refrigerant suction or discharge direction in the passage.

Moreover, the passages through which the refrigerant discharged from the first compression mechanism unit flows includes an inner passage through which the compressed refrigerant is discharged into the shell and a mid-pressure passage through which the compressed refrigerant is discharged to the valve.

Further, the passage through which the refrigerant introduced from the second compression mechanism unit flows is selectively connected by the valve to either a passage connecting the accumulator to the valve or a mid-pressure passage through which the compressed refrigerant is discharged from the first compression mechanism unit to the valve.

Furthermore, the passages through which the refrigerant to be sucked into the second compression mechanism unit flows includes a passage into which the refrigerant is sucked from the accumulator and a passage into which the refrigerant compressed in the first compression mechanism unit is sucked.

Still furthermore, the frequency variable compressor further includes a control unit controlling the opening and closing of the valve, wherein the control unit controls the valve to compress the refrigerant in the 2-stage rotary compressor type when a small cooling capacity is required of the compressor and in the twin rotary compressor type when a large cooling capacity is required of the compressor.

Still furthermore, the control unit controls the speed of the frequency variable motor according to a cooling capacity required of the compressor.

Still furthermore, when the compressor is operated at a speed lower than a speed in which the frequency variable motor has the maximum efficiency, the control unit controls the valve such that the first and second compression mechanism units compress the refrigerant in the 2-stage rotary compressor type.

According to a still further aspect of the present invention, there is provided a frequency variable compressor, including: a shell defining a hermetic space; an accumulator temporarily storing refrigerant before introducing the refrigerant into the shell; a first compression mechanism unit positioned in the shell, including a rolling piston, a cylinder, a refrigerant suction hole, a refrigerant discharge hole and a vane, and compressing refrigerant; a second compression mechanism unit positioned in the shell, including a rolling piston, a cylinder, a refrigerant suction hole, a refrigerant discharge hole and a vane, and compressing refrigerant; a frequency variable motor positioned in the shell and transferring power to the rolling pistons of the first and second compression mechanism units through a rotating shaft; a first suction passage through which the refrigerant is sucked into the first compression mechanism unit; a first discharge passage through which the refrigerant is discharged from the first compression mechanism unit; a second suction passage through which the refrigerant is sucked into the second compression mechanism unit; a mid-pressure passage connecting the second suction passage to the first discharge passage; and a valve provided on the mid-pressure passage and the second suction passage, connecting and disconnecting some part of the second suction passage to/from the mid-pressure passage, and closing and opening the rest of the second suction passage.

In addition, the valve closes the rest of the second suction passage when some part of the second suction passage is connected to the mid-pressure passage, and opens the rest of the second suction passage when some part of the second suction passage is disconnected from the mid-pressure passage.

Moreover, the frequency variable compressor further includes a first discharge valve provided at one end of the first discharge passage and opening the first discharge passage over a determined pressure to discharge the refrigerant into the shell.

Further, the opening pressure of the first discharge valve is determined not to open the first discharge valve when the mid-pressure passage is connected to some part of the second suction passage, such that the refrigerant discharged from the first compression mechanism unit is sucked into the second suction passage.

Furthermore, the frequency variable compressor further includes a lower bearing positioned below the first compression mechanism unit and temporarily storing the refrigerant discharged from the first compression mechanism unit, the first discharge passage being connected to the lower bearing.

Still furthermore, the frequency variable compressor further includes a mid-pressure discharge valve installed at the lower bearing and opened when the refrigerant compressed in the first compression mechanism unit has a pressure over a determined value.

Still furthermore, the mid-pressure passage is connected to the lower bearing.

Still furthermore, the first discharge passage penetrates through the first compression mechanism unit and the second compression mechanism unit.

Still furthermore, the mid-pressure passage is defined by a pipe having both ends positioned on the first discharge passage and the valve, respectively.

Still furthermore, the pipe defining the mid-pressure passage has one end inserted into the second compression mechanism unit and is connected to the first discharge passage defined in the second compression mechanism unit.

Still furthermore, the pipe defining the mid-pressure passage is upwardly extended from the second compression mechanism unit and connected to the valve.

According to a still further aspect of the present invention, there is provided a frequency variable compressor, including: a shell defining a hermetic space; an accumulator temporarily storing refrigerant before introducing the refrigerant into the shell; a first compression mechanism unit positioned in the shell, including a rolling piston, a cylinder, a refrigerant suction hole, a refrigerant discharge hole and a vane, and compressing refrigerant; a second compression mechanism unit positioned in the shell, including a rolling piston, a cylinder, a refrigerant suction hole, a refrigerant discharge hole and a vane, and compressing refrigerant; a frequency variable motor positioned in the shell and transferring power to the rolling pistons of the first and second compression mechanism units through a rotating shaft; a first suction passage through which the refrigerant is sucked into the first compression mechanism unit; a first discharge passage through which the refrigerant is discharged from the first compression mechanism unit into the shell; a second suction passage through which the refrigerant is sucked into the second compression mechanism unit; and a 4-way valve controlled such that the refrigerant discharged to the first discharge passage is sucked into the second suction passage or discharged into the shell, two valve holes being positioned on the second suction passage, the other two valve holes being positioned on the first discharge passage.

In addition, the frequency variable compressor further includes a check valve positioned on the first discharge passage.

Moreover, the frequency variable compressor further includes a check valve positioned on the second suction passage.

According to a still further aspect of the present invention, there is provided a frequency variable compressor, including: a shell defining a hermetic space; a plurality of compression mechanism units positioned in the shell and compressing refrigerant; a frequency variable motor positioned in the shell and transferring power to the plurality of compression mechanism units through a rotating shaft; and a valve controlling the suction and discharge directions with respect to the plurality of compression mechanism units such that the plurality of compression mechanism units compress the refrigerant in a twin rotary compressor type or a 2-stage rotary compressor type.

According to a still further aspect of the present invention, there is provided a frequency variable compressor, including: a shell defining a hermetic space; a first compression mechanism unit positioned in the shell, including a rolling piston, a cylinder, a refrigerant suction hole, a refrigerant discharge hole and a vane, and compressing refrigerant; a second compression mechanism unit positioned in the shell, including a rolling piston, a cylinder, a refrigerant suction hole, a refrigerant discharge hole and a vane, and compressing refrigerant; a lower bearing positioned below the first compression mechanism unit and temporarily storing the refrigerant discharged from the first compression mechanism unit; an upper bearing positioned over the second compression mechanism unit; a first discharge port positioned in the upper bearing and opened when the refrigerant discharged from the first compression mechanism unit has a pressure over a determined value; a second discharge port positioned in the upper bearing and opened when the refrigerant discharged from the second compression mechanism unit has a pressure over a determined value; an inner passage connecting the lower bearing to the first discharge port; an accumulator temporarily storing the refrigerant before introducing the refrigerant into the shell; a 4-way valve selecting a refrigerant discharge passage of the first compression mechanism unit and a refrigerant suction passage of the second compression mechanism unit such that the first compression mechanism unit and the second compression mechanism unit compress the refrigerant in a twin rotary compressor type or a 2-stage rotary compressor type; a first suction pipe providing a refrigerant passage between the accumulator and the refrigerant suction hole of the first compression mechanism unit; a mid-pressure suction pipe providing a refrigerant passage between the lower bearing and the 4-way valve; a second suction pipe providing a refrigerant passage between the accumulator and the 4-way valve; and a third suction pipe providing a refrigerant passage between the 4-way valve and the refrigerant suction hole of the second compression mechanism unit.

According to a still further aspect of the present invention, there is provided a frequency variable compressor, including: a shell defining a hermetic space; a first compression mechanism unit positioned in the shell, including a rolling piston, a cylinder, a refrigerant suction hole, a refrigerant discharge hole and a vane, and compressing refrigerant; a second compression mechanism unit positioned in the shell, including a rolling piston, a cylinder, a refrigerant suction hole, a refrigerant discharge hole and a vane, and compressing refrigerant; an inner passage formed such that the refrigerant compressed in the first compression mechanism unit is discharged into the shell through the first compression mechanism unit and the second compression mechanism unit; an accumulator temporarily storing the refrigerant before introducing the refrigerant into the shell; a 4-way valve selecting a refrigerant discharge passage of the first compression mechanism unit and a refrigerant suction passage of the second compression mechanism unit such that the first compression mechanism unit and the second compression mechanism unit compress the refrigerant in a twin rotary compressor type or a 2-stage rotary compressor type; a first suction pipe providing a refrigerant passage between the accumulator and the refrigerant suction hole of the first compression mechanism unit; a mid-pressure suction pipe providing a refrigerant passage between the inner passage and the 4-way valve; a second suction pipe providing a refrigerant passage between the accumulator and the 4-way valve; and a third suction pipe providing a refrigerant passage between the 4-way valve and the refrigerant suction hole of the second compression mechanism unit.

In addition, the mid-pressure suction pipe penetrates through an upper portion of the shell and is fixed by the shell.

According to a still further aspect of the present invention, there is provided a frequency variable compressor, including: a shell defining a hermetic space; a first compression mechanism unit positioned in the shell, including a rolling piston, a cylinder, a refrigerant suction hole, a refrigerant discharge hole and a vane, and compressing refrigerant; a second compression mechanism unit positioned in the shell, including a rolling piston, a cylinder, a refrigerant suction hole, a refrigerant discharge hole and a vane, and compressing refrigerant; a lower bearing positioned below the first compression mechanism unit and temporarily storing the refrigerant discharged from the first compression mechanism unit; an upper bearing positioned over the second compression mechanism unit; a discharge port positioned in the upper bearing and opened when the refrigerant discharged from the second compression mechanism unit has a pressure over a determined value; an accumulator temporarily storing the refrigerant before introducing the refrigerant into the shell; a first suction pipe providing a refrigerant passage between the accumulator and the refrigerant suction hole of the first compression mechanism unit; a first discharge pipe having one end connected to the lower bearing and providing a passage through which the refrigerant compressed in the first compression mechanism unit is discharged into the shell; a second suction pipe providing a refrigerant passage between the accumulator and the refrigerant suction hole of the second compression mechanism unit; and a 4-way valve controlling the discharge direction such that the refrigerant flowing through the first discharge pipe flows to either the shell or the second compression mechanism unit, two valve holes being positioned on the first discharge pipe, the other two valve holes being positioned on the second suction pipe.

In addition, a counter-flow prevention valve is installed at a portion of the first discharge pipe connecting the 4-way valve to the shell.

Moreover, a counter-flow prevention valve is installed at a portion of the second suction pipe connecting the 4-way valve to the accumulator.

According to a still further aspect of the present invention, there is provided a control method of a frequency variable compressor, including: a first step of receiving, at a control unit, an input of a required cooling capacity; a second step of controlling a valve to select either a twin compression method or a 2-stage compression method as a driving method of a compression mechanism unit; and a third step of controlling a driving speed of a frequency variable motor.

According to a still further aspect of the present invention, there is provided a control method of a frequency variable compressor, including: a first step of receiving, at a control unit, an input of a required cooling capacity; a second step of comparing the required cooling capacity with a compression capacity obtained by a twin compression method at a speed in which a frequency variable motor has the maximum efficiency; and a third step of selecting either the twin compression method or a 2-stage compression method as a driving method of a compression mechanism unit according to the result of the second step.

In addition, the control method further includes a fourth step of controlling a driving speed of the frequency variable motor.

Moreover, the third step controls a 4-way valve to select the driving method of the compression mechanism unit.

Advantageous Effects

In the frequency variable compressor and the control method thereof according to the present invention, although a small compression capacity is required, the compressor can be operated in the mid to high speed operation range in which the frequency variable motor has relatively high efficiency, unlike the conventional twin compressor.

Additionally, in the frequency variable compressor and the control method thereof according to the present invention, the compressor compresses the refrigerant by the 2-stage compression method at a low operating frequency in which efficiency of the frequency variable motor is degraded, and thus reduces an over-compression loss more than by a one-stage compression method or a twin compression method. There is an advantage of improving efficiency of the compressor during the low-capacity compression operation of relatively high using frequency.

Moreover, in the frequency variable compressor and the control method thereof according to the present invention, when a cooling capacity required for compression increases, the compressor converts the compression method into the twin compression method and raises the operating frequency of the frequency variable motor to increase the compression capacity. Accordingly, it is possible to increase the compressible capacity range of the compressor and considerably improve energy efficiency of the compressor.

DESCRIPTION OF DRAWINGS

FIG. 1 is a view of a conventional twin rotary compressor;

FIG. 2 is a view of a conventional 2-stage rotary compressor;

FIG. 3 is a graph of efficiency and yearly operating time of a compressor including a conventional DC frequency variable motor as a motor unit by cooling and heating loads (operating frequencies);

FIG. 4 is a graph of changes in an operating frequency of a general frequency variable compressor by the time elapsed;

FIG. 5 is a graph of efficiency of a frequency variable compressor according to the present invention;

FIGS. 6 and 7 are views of a frequency variable compressor according to a first embodiment of the present invention;

FIGS. 8 and 9 are views of a frequency variable compressor according to a second embodiment of the present invention;

FIGS. 10 and 11 are views of a frequency variable compressor according to a third embodiment of the present invention; and

FIG. 12 is a graph of the comparison of efficiency between a frequency variable compressor according to an embodiment of the present invention and a conventional inverter compressor.

MODE FOR INVENTION

FIG. 4 is a graph of changes in an operating frequency of a general frequency variable compressor by the time elapsed. Normally, the compressor is a part of a freezing cycle of cooling apparatuses including air conditioners and refrigerators or heating apparatuses using heat pumps. The cooling apparatus or the heating apparatus is initially operated in a power mode until the ambient temperature reaches a desired temperature and in a saving mode after the ambient temperature reaches the desired temperature. The power mode is an operating mode which increases a compression capacity of the compressor to raise the cooling or heating capability of the cooling apparatus or the heating apparatus, and the saving mode is an operating mode which decreases the compression capacity of the compressor to lower the cooling or heating capability of the cooling apparatus or the heating apparatus. In the case of a frequency variable compressor using a frequency variable motor as a driving device for refrigerant compression, an operating frequency of the motor is set at a high to mid frequency (about 120 Hz to 60 Hz) in the power mode and at a mid to low frequency (about 60 Hz to 20 Hz) in the saving mode. However, the general cooling apparatus or heating apparatus is initially operated in the power mode to cause a change in temperature until the ambient temperature reaches the desired temperature, and normally operated in the saving mode to maintain the desired temperature after the ambient temperature reaches the desired temperature. Accordingly, the operating time is much longer in the saving mode than in the power mode. As described in relation to the prior art, the frequency variable compressor has the maximum efficiency in mid-frequencies (about 50 Hz to 70 Hz), generally maintains high efficiency in high frequencies (over 70 Hz), and has low efficiency in low frequencies (below 50 Hz). Therefore, it is necessary to improve efficiency of the frequency variable compressor in the low-frequency (below 50 Hz) region. The low-frequency region, the mid-frequency region and the high-frequency region may be dependent upon detailed specifications of the frequency variable motor. In general, the region in which the frequency variable motor has the maximum efficiency is set as the mid-frequency region, the region in which frequencies are lower than the mid-frequencies and efficiency of the frequency variable motor is sharply reduced is set as the low-frequency region, and the region in which frequencies are higher than the mid-frequencies and efficiency of the frequency variable motor is gradually reduced is set as the high-frequency region. The mid-frequency region is a frequency region of efficiency which is not different from the maximum efficiency of the frequency variable motor by over 5%.

The frequency variable compressor according to the present invention includes a plurality of compression chambers. The compression chamber is a space in which the sucked refrigerant is compressed. In the case of a rotary compressor, the compression chamber is a space defined in a compression mechanism unit including a cylinder and a rolling piston. One compression chamber may be defined in one compression mechanism unit, or two or more compression chambers may be defined in one compression mechanism unit.

According to the present invention, a plurality of compression chambers may be defined in one compression mechanism unit, compression chambers as many as compression mechanism units may be defined in the plurality of compression mechanism units, and compression chambers more than compression mechanism units may be defined in the plurality of compression mechanism units.

The process in which the refrigerant is sucked into the plurality of compression chambers, compressed therein and discharged therefrom may be performed in parallel. The representative examples of compressing the refrigerant in parallel in the plurality of compression chambers are a twin (double) compressor, a triple compressor, and so on. In addition, the refrigerant may be sucked into one of the plurality of compression chambers, compressed therein, sucked again into another compression chamber, compressed therein and discharged therefrom. The representative examples of sequentially compressing the refrigerant in the plurality of compression chambers are a 2-stage compressor, a 3-stage compressor, and so on.

The frequency variable compressor according to the present invention compresses the refrigerant in parallel in the plurality of compression chambers when it is operated over a mid-frequency and sequentially compresses the refrigerant in the plurality of compression chambers when it is operated at a low frequency. Generally, when some of the refrigerant is compressed over a necessary pressure, an over-compression loss occurs in the compressor.

When the refrigerant is compressed by multiple stages, the compression loss occurs merely in the final-stage compression. Moreover, the volume of the refrigerant to be compressed is smaller in the final stage of the multi-stage compression than the 1-stage compression or the parallel compression, and thus the compression loss is also smaller. When the compressor is operated at a frequency below a mid frequency, the multi-stage compression improves efficiency of the compressor more than the 1-stage compression or the multiple compression. Therefore, when operated at a low frequency, the frequency variable compressor according to the present invention compresses the refrigerant by the multi-stage compression method for sequentially compressing the refrigerant in the plurality of compression chambers.

The frequency variable compressor according to the present invention includes a plurality of compression chambers in a shell which are unit spaces for refrigerant compression, and a frequency variable motor supplying a driving force to a compression mechanism unit to compress the refrigerant in the compression chamber. As discussed earlier, the compression chamber is provided in the compression mechanism unit. One or plural compression chambers may be defined in one compression mechanism unit. A refrigerant suction passage through which the refrigerant is introduced into the compression chamber and a refrigerant discharge passage through which the refrigerant is discharged from the compression chamber to the shell must be provided to compress the refrigerant in the compression chamber and discharge the refrigerant therefrom.

At least one (hereinafter, referred to as ‘first compression chamber’) of the plurality of compression chambers includes a first discharge passage through which the compressed refrigerant is discharged into the shell and a mid-pressure passage through which the compressed refrigerant is sucked into at least another one (hereinafter, referred to as ‘second compression chamber’) of the plurality of compression chambers. The mid-pressure passage connected to the first compression chamber is selectively connected to a second suction passage connected to the second compression chamber. That is, the mid-pressure passage and the second suction passage can be connected or disconnected to/from each other by a valve. In addition, the second suction passage is divided into two parts at the valve-connected section. In other words, at the valve-connected section, the second suction passage can be divided into a part (first part) connected directly to the second compression chamber and allowing the refrigerant to be sucked into the second compression chamber and a part (second part) connected to the first part and introducing low-pressure refrigerant.

When the valve disconnects the mid-pressure passage from the second suction passage, the refrigerant discharged from the first compression chamber cannot be sucked into the second suction passage through the mid-pressure passage, and thus is discharged into the shell through the first discharge passage.

Moreover, in parallel to this, the low-pressure refrigerant is sucked into the second suction passage, compressed in the second compression chamber, and discharged into the shell. On the contrary, when the valve connects the mid-pressure passage to the first part of the second suction passage, the valve prevents the low-pressure refrigerant from being sucked into the second part of the second suction passage and allows the refrigerant compressed in the first compression chamber to be sucked into the first part of the second suction passage through the mid-pressure passage. The refrigerant compressed in the first compression chamber is not discharged into the shell through the first discharge passage but sucked into the second compression chamber through the mid-pressure passage due to the suction pressure in the second compression chamber. The refrigerant sucked into the second compression chamber may be re-compressed and discharged into the shell. Further, the refrigerant compressed in the second compression chamber may be sucked into another one (third compression chamber) of the plurality of compression chambers, compressed as the third stage, and then discharged into the shell.

There are no limitations on the construction of the plurality of compression chambers, the suction and discharge passages, the mid-pressure passage and the valve so far as the multi-stage compression and the multiple compression can be selectively performed in the plurality of compression chambers by the valve. Additionally, the 2-stage compression may occur in the first compression chamber and the second compression chamber, the 2-stage compression may occur in the third compression chamber and the fourth compression chamber, and each 2-stage compression may be performed in parallel. Further, the 3-stage compression and the 1-stage compression may be performed in parallel. That is, the compression may be implemented in various forms.

FIG. 5 is a graph of efficiency of a frequency variable compressor according to the present invention. Here, the frequency variable compressor includes two compression mechanism units, in which one compression chamber is defined in each compression mechanism unit. As explained above, when the operating frequency of the frequency variable compressor according to the present invention was a low frequency of 20 Hz, the 2-stage compression method improved efficiency more than the twin compression method by about 10 to 15%.

However, when the compressor was operated in the high frequency region over 80 Hz, the twin compression method was more efficient than the 2-stage compression method. When the compressor was operated at a high frequency, the 2-stage compression method became less efficient than the twin compression method due to a loss caused by a valve. Accordingly, in order to improve efficiency of the compressor in the low-frequency region, when the operating frequency of the frequency variable compressor exists in the low-frequency region, it is preferable to control the valve to compress the refrigerant by the 2-stage compression method. That is, when the operating frequency of the frequency variable compressor exists in the low-frequency region, it is preferable to perform the multi-stage compression in the plurality of compression chambers.

Hereinafter, an embodiment of a frequency variable compressor including two compression mechanism units will be described, in which one compression chamber is defined in each compression mechanism unit.

FIGS. 6 and 7 are views of a frequency variable compressor according to a first embodiment of the present invention. The frequency variable compressor according to the first embodiment of the present invention includes two compression mechanism units and compresses refrigerant by a twin compression method in a power mode and by a 2-stage compression method in a saving mode.

The frequency variable compressor includes a shell 100 forming the external appearance of the compressor, a DC variable speed frequency variable motor 200 (hereinafter, referred to as ‘frequency variable motor’) is installed in the shell 100 as a motor unit, and a rotating shaft 300 transferring a rotational force of the frequency variable motor 200 is connected to the frequency variable motor 200. According to the first embodiment of the present invention, the frequency variable motor 200 is positioned on the upper side in the shell 100, and the rotating shaft 300 is downwardly extended from the frequency variable motor 200. A compression mechanism unit 400 is installed below the frequency variable motor 200, receives power from the frequency variable motor 200 through the rotating shaft 300, and compresses the refrigerant. The compression mechanism unit 400 includes a first compression mechanism unit 410 and a second compression mechanism unit 420 which are rotary compression mechanisms. That is, the first compression mechanism unit 410 and the second compression mechanism unit 420 include cylinders 411 and 421 providing spaces for refrigerant compression, rolling pistons 412 and 422, refrigerant suction holes 410 h and 420 h, refrigerant discharge holes 410 d and 420 d, and vanes (not shown), respectively. The first compression mechanism unit 410 and the second compression mechanism unit 420 can compress a determined amount of refrigerant, respectively.

A lower bearing 500 is installed below the first compression mechanism unit 410, and an upper bearing 600 is installed over the second compression mechanism unit 420. A mid-pressure discharge valve 510 opened when the refrigerant compressed in the first compression mechanism unit 410 has a pressure over a determined value is installed at the lower bearing 500. The mid-pressure refrigerant discharged through the mid-pressure discharge valve 510 temporarily stays in the lower bearing 500. A first discharge port 610 discharging the refrigerant temporarily stored in the lower bearing 500 into the shell 100 over a determined pressure and a second discharge port 620 discharging the refrigerant compressed in the second compression mechanism unit 420 into the shell 100 are formed in the upper bearing 600. The first discharge port 610 is connected to an inner space of the lower bearing 500 through a discharge passage 820, and the discharge passage 820 provides a refrigerant movement path from the lower bearing 500 to the first discharge port 610. The discharge passage 820 may be formed as an inner passage penetrating through the cylinder 411 of the first compression mechanism unit 410 and the cylinder 421 of the second compression mechanism unit 420 and connecting the lower bearing 500 to the first discharge port 610.

The refrigerant is sucked from an accumulator 900 into the first compression mechanism unit 410 and the second compression mechanism unit 420 through suction passages 810, 840 and 850. The refrigerant is introduced from another apparatus constituting the freezing cycle with the frequency variable compressor into the accumulator 900 and temporarily stored therein. The first suction passage 810 and the second suction passage 840 and 850 are connected to the accumulator 900. The refrigerant is divided into liquid refrigerant and gas refrigerant in the accumulator 900 and only the gas-phase refrigerant is sucked into the first suction passage 810 and the second suction passage 840 and 850. In addition, a mid-pressure passage 830 connects a part 850 of the second suction passage 840 and 850 to the lower bearing 500 such that the refrigerant compressed first in the first compression mechanism unit 410 is sucked into the second compression mechanism unit 420 through the part 850 of the second suction passage 840 and 850.

Moreover, the double capacity variable inverter compressor according to this embodiment includes a 4-way valve 700 connected to the mid-pressure passage 830 and also connected to the middle of the second suction passage 840 and 850 to divide the second suction passage 840 and 850 into two parts 840 and 850. The 4-way valve 700 serves to selectively connect either the other part 840 of the second suction passage 840 and 850 or the mid-pressure passage 830 to the part 850 of the second suction passage 840 and 850 connected to the second mechanism unit 420. Irrespective of the control of the valve 700, the refrigerant is always sucked into the first compression mechanism unit 410 through the first suction passage 810 which is not connected to the valve 700.

A control unit (not shown) controls the valve 700 such that the compression mechanism unit 400 compresses the refrigerant by the twin compression method or the 2-stage compression method. Additionally, the control unit (not shown) not only controls the valve 700 but also controls the speed of the frequency variable motor 200. The control unit (not shown) receives an input of a cooling capacity required of an indoor unit or the like of the freezing/heating cycle including the double capacity variable inverter compressor or receives information on the cooling capacity and controls the speed of the frequency variable motor 200 or controls the compression method of the compression mechanism unit 400 using the valve 700. That is, the first compression mechanism unit 410 and the second compression mechanism unit 420 may adopt the twin rotary compressor type in which each of the first compression mechanism unit 410 and the second compression mechanism unit 420 compresses a determined amount of refrigerant and discharges the compressed refrigerant into the shell 100, or the 2-stage rotary compressor type in which the first compression mechanism unit 410 compresses the refrigerant and the second compression mechanism unit 420 re-compresses the refrigerant and discharges the 2-stage compressed refrigerant into the shell 100.

FIG. 6 illustrates a state where the compression mechanism unit 400 compresses the refrigerant in the twin rotary compressor type, one part 850 of the second suction passage 840 and 850 being connected to the other part 840, the mid-pressure passage 830 being closed. The refrigerant is sucked from the accumulator 900 into the first compression mechanism unit 410 through the first suction passage 810 and into the second compression mechanism unit 420 through the second suction passage 840 and 850 at the same time. The refrigerant sucked into the cylinders 411 and 421 is compressed by the rolling pistons 412 and 422 rotated by power of the frequency variable motor 200 transferred through the rotating shaft 300. The refrigerant compressed over a determined pressure in the first compression mechanism unit 410 opens the mid-pressure discharge valve 510 and is discharged to the lower bearing 500 through the refrigerant discharge hole 410 d. Since the mid-pressure passage 830 has been closed by the valve 700, the refrigerant cannot be introduced into the part of the second suction passage 840 and 850.

Therefore, the refrigerant temporarily stored in the lower bearing 500 is discharged into the shell 100 through the first discharge port 610 along the discharge passage 820. Here, a first discharge valve 610 v is installed on the first discharge port 610 to discharge the refrigerant into the shell 100 through the first discharge port 610 when the refrigerant has a pressure over a determined value. Meanwhile, the second compression mechanism unit 420 compresses the refrigerant sucked through the second suction passage 840 and 850 and discharges the refrigerant into the shell 100 through the second discharge port 620. A second discharge valve 620 v is installed on the second discharge port 620 to discharge the refrigerant into the shell 100 when the refrigerant has a pressure over a determined value. As described above, each of the first compression mechanism unit 410 and the second compression mechanism unit 420 compresses the determined amount of refrigerant and discharges the refrigerant into the shell 100. The total compression capacity of the refrigerant is equal to the sum of the compression capacity of the first compression mechanism unit 410 and the compression capacity of the second compression mechanism unit 420. The total compression capacity of the compressor can be controlled according to the speed (frequency) of the frequency variable motor 200.

FIG. 7 illustrates a state where the compression mechanism unit 400 compresses the refrigerant in the 2-stage compressor type, one part 850 of the second suction passage 840 and 850 being disconnected from the other part 840 and connected to the mid-pressure passage 830. The refrigerant stored in the accumulator 900 is sucked into the first compression mechanism unit 410 through the first suction passage 810, compressed therein, and discharged to the lower bearing 500. Thereafter, since the mid-pressure passage 830 has been connected to the part 850 of the second suction passage 840 and 850 by the valve 700, the refrigerant discharged to the lower bearing 500 is sucked into the second compression mechanism unit 420 through the mid-pressure passage 830 and the part 850 of the second suction passage 840 and 850. A sound pressure is generated in the cylinder 421 due to the rolling piston 422 fitted onto the rotating shaft 300 and rotated in the cylinder 421, and operated as a refrigerant suction pressure. Accordingly, the refrigerant discharged to the lower bearing 500 is not discharged into the shell 100 through the discharge passage 820 as shown in FIG. 4, but sucked into the second compression mechanism unit 420 through the mid-pressure passage 830 and the part 850 of the second suction passage 840 and 850. The second compression mechanism unit 420 re-compresses the refrigerant compressed in the first compression mechanism unit 410 and discharges the 2-stage compressed refrigerant into the shell 100 through the second discharge port 620 of the upper bearing 600.

Here, the first discharge valve 610 v installed on the first discharge port 610 is preferably a counter-flow prevention valve such that the refrigerant in the shell 100 is not sucked into the second compression mechanism unit 420 again through the first discharge port 610—the discharge passage 820—the lower bearing 500—the mid-pressure passage 830 due to the suction pressure of the second compression mechanism unit 420.

FIGS. 8 and 9 are views of a frequency variable compressor according to a second embodiment of the present invention. A shell 100, a frequency variable motor 200, a rotating shaft 300, a compression mechanism unit 400, a lower bearing 500, an upper bearing 600, a valve 700 and an accumulator 900 are the same as those of the first embodiment of the present invention, and thus detailed description thereof will be omitted.

According to the second embodiment of the present invention, a mid-pressure passage 830′ penetrates an upper portion of the shell 100. This can significantly reduce piping vibration generated in the mid-pressure passage 830′. Moreover, in the drawings, a discharge passage 820 and a first discharge port 610 are formed in the opposite direction to a mid-pressure discharge valve 510 and a second discharge port 620 such that the discharge passage 820 and the first discharge port 610 do not overlap with the mid-pressure discharge valve 510 and the second discharge port 620. However, actually, the discharge passage 820 and the first discharge port 610 are very close to the mid-pressure discharge valve 510 and the second discharge port 620. If the discharge passage 820 is distant from the mid-pressure discharge valve 510, i.e., if the discharge passage 820 is distant from a discharge hole 410 d of a first compression mechanism unit 410, when the refrigerant flows, its pressure loss is generated in the lower bearing 500. Therefore, if the mid-pressure passage 830′ is connected to the discharge passage 820, i.e., inserted into a cylinder 421 of a second compression mechanism unit 420, the length of the mid-pressure passage 830′ can be considerably reduced.

Thus, when the refrigerant flows through the mid-pressure passage 830′, its pressure loss can be reduced.

FIG. 8 illustrates a state where the compressor is operated as a twin rotary compressor, and FIG. 9 illustrates a state where the compressor is operated as a 2-stage rotary compressor. The construction of the second embodiment is the same as that of the first embodiment except the position of the mid-pressure passage 830′, and thus the operation methods of the twin compressor and the 2-stage compressor are the same as those of the first embodiment.

FIGS. 10 and 11 are views of a frequency variable compressor according to a third embodiment of the present invention. FIG. 10 illustrates a state where the compressor compresses refrigerant by a twin compression method, and FIG. 11 illustrates a state where the compressor compresses refrigerant by a 2-stage compression method.

Like the first and second embodiments, the frequency variable compressor according to the third embodiment of the present invention includes a shell 100, a frequency variable motor 200, a rotating shaft 300, a compression mechanism unit 400, a lower bearing 500, an upper bearing 600, a valve 700 and an accumulator 900. The third embodiment is the same as the first and second embodiments except the construction of suction passages and discharge passages.

First, the driving by the twin compression method will be described with reference to FIG. 10. The refrigerant is sucked into a first compression mechanism unit 410 through a first suction passage 810, compressed therein, and discharged to the lower bearing 500. Next, the compressed refrigerant flows to the valve 700 through a mid-pressure passage 830″ connected to the lower bearing 500. The mid-pressure passage 830″ is disconnected from a part 850 of a second suction passage 840 and 850 by the valve 700, and the other part 840 of the second suction passage 840 and 850 communicates with the part 850 of the second suction passage 840 and 850. The refrigerant of the mid-pressure passage 830″ is discharged into the shell 100 through a first discharge passage 820′ connected to the valve 700. A check valve 800 v is installed on the first discharge passage 820′ to prevent the refrigerant from being introduced from the shell 100 to the first discharge passage side 820′.

In the meantime, the refrigerant is sucked from the accumulator 900 to a second compression mechanism unit 420 through the second suction passage 840 and 850, compressed therein, and discharged into the shell 100.

The driving by the 2-stage compression method will be described with reference to FIG. 11. The refrigerant is sucked into the first compression mechanism unit 410 through the first suction passage 810, compressed therein, and discharged to the lower bearing 500. Next, the compressed refrigerant flows to the valve 700 through the mid-pressure passage 830″ connected to the lower bearing 500. The valve 700 is controlled to allow the part 850 of the second suction passage 840 and 850 and the mid-pressure passage 830″ to communicate with each other and to close the other part 840 of the second suction passage 840 and 850. The mid-pressure refrigerant sucked into the second compression mechanism unit 420 through the mid-pressure passage 830″ and the part 850 of the second suction passage 840 and 850 is compressed into a high pressure and discharged into the shell 100 through a second discharge port 620. In the third embodiment of the present invention, a first discharge port is not specially formed. Meanwhile, the check valve 800 v allows the refrigerant to flow from the valve 700 into the shell 100 but disallows the refrigerant to flow from the shell 100 into the valve side 700.

Therefore, it is possible to prevent the refrigerant from flowing backward from the shell 100 having a higher pressure than the mid-pressure passage 830″ or the discharge passage 820 to the discharge passage 820. Generally, the frequency variable motor 200 has the maximum efficiency in the middle of its speed (operating frequency) range. In addition, the frequency variable motor 200 has much higher efficiency in the mid to high speed operation than the low to mid-speed operation. Accordingly, a control unit (not shown) preferably controls the frequency variable motor 200 to perform the mid to high speed operation.

FIG. 12 is a graph of the comparison of efficiency between a frequency variable compressor according to an embodiment of the present invention and a conventional inverter compressor. When it is assumed that first and second compression mechanism units 410 and 420 have the same compression capacity, the 2-stage compression method can reduce the compression capacity by about 50% as compared with the twin compression method. Therefore, when a capacity compressed by operating the conventional compressor in the low to mid speed section by a frequency variable motor 200 is compressed by the 2-stage compression method, it can be compressed in the mid to high speed section.

For example, it is assumed that a capacity compressed by the twin compression method at a speed in which the frequency variable motor 200 has maximum efficiency is ‘100’ and a compression capacity of the first and second compression mechanism units 410 and 420 is ‘50’, respectively. If a required cooling capacity is ‘70’, when the 2-stage compression method is used, the compression capacity of the compression mechanism unit 400 is about ‘50’.

Accordingly, when the speed of the frequency variable motor 200 is raised to 140%, the compressor can perform the high-speed operation. As a result, the compressor can be operated in the mid to high speed operation range in which the frequency variable motor 200 has relatively high efficiency. Additionally, when a large cooling or heating load is generated in a cooling or heating apparatus to which the compressor is connected, i.e., when a large compression capacity is required of the compressor, the compression capacity can be increased by converting the compression method into the twin compression method and raising the operating frequency of the frequency variable motor. Therefore, the frequency variable compressor according to the present invention can increase the compressible capacity range and considerably improve energy efficiency.

Further, the 2-stage compression method has a smaller over-compression loss than the 1-stage compression method or the twin compression method. When the frequency variable compressor is operated at a low speed, i.e., in a low-frequency region, if the valve is controlled such that the refrigerant is compressed in the plurality of compression chambers by multiple steps, it is possible to reduce the over-compression loss. Furthermore, the control unit controls the operating frequency of the frequency variable motor to adjust the capacity of the refrigerant compressed in the compressor to the compression capacity required of the compressor. When the operating frequency enters the low-frequency region, the control unit controls the valve to compress the refrigerant in the plurality of compression chambers by multiple steps. It is more effective to improve efficiency of the compressor at an operating frequency of the low-frequency region having relatively long operating time than the other operating frequency regions.

Hereinafter, a control method of a frequency variable compressor according to the present invention will be described. As discussed earlier, in the case of a compressor provided in a cooling apparatus or a heating apparatus, a refrigerant compression capacity per unit time required of the compressor is large at an initial stage but small after the ambient temperature reaches a desired temperature. Therefore, as illustrated in FIG. 4, an operating frequency of the conventional frequency variable compressor is gradually reduced with the passage of time. After the ambient temperature reaches a desired temperature, the compressor is operated at a low frequency of 30 Hz to 40 Hz.

The frequency variable compressor according to the present invention starts to be operated by the multiple compression method such as the twin compression method because a required compression capacity is large at an initial stage of the operation. In addition, an operating frequency of the frequency variable compressor of the present invention is controlled similarly to the operating frequency of the conventional frequency variable compressor of FIG. 4 until the ambient temperature reaches a desired temperature. Thereafter, as the compression capacity required of the frequency variable compressor of the present invention decreases, a control unit controlling a frequency variable motor adjusts the operating frequency of the motor to a low frequency. When the operating frequency becomes a low frequency (about 20 Hz to 40 Hz), the control unit controls the connection of a suction passage, a discharge passage and a mid-pressure passage connected to a plurality of compression chambers and changes the flow of the refrigerant, thereby compressing the refrigerant by the multi-stage compression method.

A control method of a frequency variable compressor according to another embodiment of the present invention will be described. First, a control unit receives an input of a required cooling capacity from another apparatus of a cycle including the frequency variable compressor or receives information on the input required cooling capacity. The control unit compares the required cooling capacity with a compression capacity obtained by the twin compression method at a mid speed (a speed in which a frequency variable motor has the maximum efficiency). If the required cooling capacity is equal to or greater than the compression capacity obtained by the twin compression method at the mid speed, the control unit controls a valve to operate a compression mechanism unit by the twin compression method. If the required cooling capacity is smaller than the compression capacity obtained by the twin compression method at the mid speed, the control unit controls the valve to operate the compression mechanism unit by the 2-stage compression method.

After determining either the twin compression method or the 2-stage compression method as the compression method, the control unit controls the speed of the frequency variable motor to generate the compression capacity equivalent to the required cooling capacity.

While the present invention has been illustrated and described in connection with the accompanying drawings and the preferred embodiments, the present invention is not limited thereto and is defined by the appended claims.

Therefore, it will be understood by those skilled in the art that various modifications and changes can be made thereto without departing from the spirit and scope of the invention defined by the appended claims. 

1. A frequency variable compressor, comprising: a shell defining a hermetic space; a plurality of compression chambers provided in the shell and compressing refrigerant therein; a frequency variable motor generating power to compress the refrigerant in the compression chamber; and a valve controlling the flow of the refrigerant sucked into and discharged from the plurality of compression chambers to sequentially or concurrently compress the refrigerant in the plurality of compression chambers.
 2. The frequency variable compressor of claim 1, wherein the plurality of compression chambers are formed in a compression mechanism unit including a rolling piston and a cylinder.
 3. The frequency variable compressor of claim 1, wherein two or more of the plurality of compression chambers are two spaces separated by a barrier in one compression mechanism unit.
 4. The frequency variable compressor of claim 1, wherein the plurality of compression chambers are formed in two or more compression mechanism units.
 5. The frequency variable compressor of claim 1, further comprising a plurality of passages through which the refrigerant is sucked into or discharged from the plurality of compression chambers, wherein the valve changes the refrigerant suction or discharge direction in the passages.
 6. The frequency variable compressor of claim 1, further comprising a plurality of passages through which the refrigerant is sucked into or discharged from the plurality of compression chambers, wherein the valve connects or disconnects the plurality of passages to/from one another.
 7. The frequency variable compressor of claim 1, further comprising a control unit controlling the valve to sequentially compress the refrigerant in two or more of the plurality of compression chambers by multiple stages, when a frequency of the frequency variable motor is controlled at a frequency below a mid frequency.
 8. The frequency variable compressor of claim 1, wherein one or more of the plurality of compression chambers are connected to an inner passage through which the compressed refrigerant is discharged into the shell and a mid-pressure passage through which the compressed refrigerant is discharged to the valve side, and the valve connects or disconnects the mid-pressure passage to/from a passage through which the refrigerant is sucked into another of the plurality of compression chambers.
 9. A frequency variable compressor, comprising: a shell defining a hermetic space; a first compression mechanism unit positioned in the shell, including a rolling piston, a cylinder, a refrigerant suction hole, a refrigerant discharge hole and a vane, and compressing refrigerant; a second compression mechanism unit positioned in the shell, including a rolling piston, a cylinder, a refrigerant suction hole, a refrigerant discharge hole and a vane, and compressing refrigerant; a frequency variable motor positioned in the shell and transferring power to the rolling pistons of the first and second compression mechanism units through a rotating shaft; a first suction passage through which the refrigerant is sucked into the first compression mechanism unit; a first discharge passage through which the refrigerant is discharged from the first compression mechanism unit; a second suction passage through which the refrigerant is sucked into the second compression mechanism unit; a mid-pressure passage connecting the second suction passage to the first discharge passage; and a valve provided on the mid-pressure passage and the second suction passage, connecting and disconnecting some part of the second suction passage to/from the mid-pressure passage, and closing and opening the rest of the second suction passage.
 10. A frequency variable compressor, comprising: a shell defining a hermetic space; an accumulator temporarily storing refrigerant before introducing the refrigerant into the shell; a first compression mechanism unit positioned in the shell, including a rolling piston, a cylinder, a refrigerant suction hole, a refrigerant discharge hole and a vane, and compressing refrigerant; a second compression mechanism unit positioned in the shell, including a rolling piston, a cylinder, a refrigerant suction hole, a refrigerant discharge hole and a vane, and compressing refrigerant; a frequency variable motor positioned in the shell and transferring power to the rolling pistons of the first and second compression mechanism units through a rotating shaft; a first suction passage through which the refrigerant is sucked into the first compression mechanism unit; a first discharge passage through which the refrigerant is discharged from the first compression mechanism unit into the shell; a second suction passage through which the refrigerant is sucked into the second compression mechanism unit; and a 4-way valve controlled such that the refrigerant discharged to the first discharge passage is selectively sucked into the second suction passage or discharged into the shell, two valve holes being positioned on the second suction passage, the other two valve holes being positioned on the first discharge passage.
 11. The frequency variable compressor of claim 10, further comprising a check valve positioned on the first discharge passage and the second suction passage.
 12. A control method of a frequency variable compressor including a plurality of compression chambers, a frequency variable motor, a valve controlling the flow of refrigerant sucked into and discharged from the plurality of compression chambers, and a control unit controlling the valve, the control method comprising, when an operating frequency of the frequency variable motor is below a mid frequency, controlling the valve to compress the refrigerant in the plurality of compression chambers by multiple stages.
 13. The control method of claim 12, comprising, when a small compression capacity is required of the compressor, controlling the operating frequency of the frequency variable motor at a low frequency.
 14. A control method of a frequency variable compressor, comprising: controlling an operating frequency of a frequency variable motor according to a required compression capacity; and when the operating frequency of the frequency variable motor is below a determined frequency, controlling a valve to compress refrigerant by either a parallel compression method for concurrently compressing the refrigerant in a plurality of compression chambers or a multi-stage compression method for sequentially compressing the refrigerant in the plurality of compression chambers.
 15. The control method of claim 14, wherein the controlling of the operating frequency of the frequency variable motor is continuously repeated according to changes in the required compression capacity and the compression method. 